Behavioral experiments in several species (see below for references) have suggested that the input to the superior colliculus from the contralateral tectum has a major influence on the visual functions mediated by this midbrain structure. Given this, it is surprising that the intertectal pathway has been studied with modern neuroanatomical techniques in only one species, the cat, and further, that the nature of information conveyed by this prjection and its influence upon the responses of the collicular cells which it innervates, has not been systematically investigated in any mammal. The experiments outlined in this proposal will use both anatomical (autoradiography and the horseradish peroxidase technique) and electrophysiological (intra- and extracellular single unit recording) methods to determine (1) the location and response characteristics of the cells of origin of the intercollicular pathway, (2) the terminal distribution of this projection and the response characteristics of the collicular cells with which it makes functional contacts, and (3) the effects of conditioning shocks delivered to the contralateral superior colliculus upon the discharges evoked from tectal cells by electrical stimulation of other afferent pathways and also on the responses obtained with "natural" stimuli. The data obtained in these studies will provide a more complete functional and anatomical description of the intertectal pathway than now exists for any species and thus should provide important insight into the manner in which this input is involved in the visual functions thought to be carried out by the colliculus.